ApplicationNo. 09/921418 filed on 08/02/2001
US Classes:188/70R, Axially and transversely movable188/1.11L, Electrical188/196R, Slack188/216, Release mechanism188/71.8, Self-adjusting means188/72.7, By inclined surface (e.g., wedge, cam or screw)188/73.2, Circumferential or circumferentially spaced188/78, Expanding188/79.51Having wear take up or compensating structure
ExaminersPrimary: Butler, Douglas C.
Attorney, Agent or Firm
International ClassesF16D 65/14 (20060101)
F16D 51/00 (20060101)
F16D 65/02 (20060101)
BACKGROUND OF THE INVENTION
This invention relates to a conical brake assembly that permits more lining material to be packaged in a brake drum than in a conventional cylindrical brake drum assembly, while reducing actuation energy requirements
Vehicle brake assemblies typically include brake linings that interact with either a brake drum to brake a vehicle. The brake linings are supported on plates and are controlled by actuators, which bring the linings into contact with the brake drum, utilizing frictional forces to stop or slow a vehicle.
These linings wear over time due to the frictional contact. For heavy duty braking applications, the linings wear out quickly and need to be replaced often. This is very expensive and results in significant vehicle down time.
Another disadvantage with brake linings is that as the linings wear, the brake becomes out of adjustment. Thus, the necessary brake pedal stroke length to actuate the brake will increase as the linings wear. To account for this, brake assemblies include slack adjusters that adjust the position of the brake linings to try to keep a constant distance between the surface of the linings and the brake drum or disc surface. These slack adjusters take up valuable packaging space and increase assembly time and cost.
Thus, it is desirable to provide a braking assembly that allows a greater amount of brake lining material to be packaged within the drum while and which utilizes an adjuster that overcomes the above mentioned deficiencies.
SUMMARY OF THE INVENTION
In a disclosed embodiment of this invention, a brake assembly includes a brake drum that is mounted for rotation about an axis. The brake drum has a conical interior cavity that defines a braking surface. A conical brake lining assembly mounted to a non-rotating axle component and presents a friction surface. A brake actuator moves the friction surface into engagement with the braking surface to brake a vehicle.
In a preferred embodiment, the brake assembly includes an adjuster mechanism that maintains a predetermined distance between the brake drum and lining assembly. The adjuster includes a first member having a threaded inner bore and a conical exterior surface. The adjuster also includes a second member having a threaded inner bore and a conical exterior surface. The first and second members are mounted on a common shaft having a threaded exterior surface. One of the threaded bores has a right handed thread and the other threaded bore has a left handed thread. The right and left handed threads engage the threaded exterior surface of the shaft to selectively draw the first and second members together linearly along the shaft to force the brake linings outwardly to maintain the predetermined distance.
This configuration allows more brake lining material to be packaged within the drum and provides a more efficient brake assembly.
These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description.
BRIEF DESCRIPTION OF THF DRAWINGS
FIG. 1 is an exploded view of the brake assembly incorporating the subject invention.
FIG. 2 is a cross-sectional view of the brake shoe assembly and adjustment mechanism, partially broken away.
FIG. 3 is a schematic view of one actuation method.
FIG. 4 is an alternate embodiment of an actuation method.
FIG. 5 is an alternate embodiment of an actuation method.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
A unique braking mechanism is shown at 10 in FIG. 1. The braking mechanism includes a conical brake drum 12 having an outer surface 14 and a frustro-conical inner cavity 16 defining a braking surface 18. The drum 12 rotates about an axis 20 with an axle wheel assembly (not shown). A brake shoe assembly, shown generally at 22, is supported by a shaft 24 and is moved linearly into the cavity 16 to brake a vehicle.
The brake shoe assembly 22 includes a brake lining 26 that is conical in shape, i.e., the brake lining 26 is of decreasing diameter from one end 28 to an opposite end 30. The brake lining 26 has an outer friction surface 32 that engages the braking surface 18 of the drum 12 to brake the vehicle. The brake lining 26 is preferably made up of four (4) brake lining block segments (only one is shown in FIG. 1) that are held together to a non-rotating wheel component with at least one resilient retainer 34. While four (4) block segments are preferred, fewer or more blocks can be utilized. Preferably, the four (4) segments are equal sections, with shoe webbing incorporating a tapered section on either end to allow for adjustment. Clearance slots are also incorporated into the web to allow for clearance of the torque rods, which are used to prevent shoe rotation during braking actuation. When a braking force is applied, the linings 26 are moved linearly into the drum 12 such that the friction surface 32 engages the braking surface 18.
An interior cavity 36, see FIG. 2, is formed within the block segments when assembled. An adjustment mechanism 38 is mounted within the cavity 36, which adjusts the block segments outwardly to maintain a predetermined distance shown at 40 between the friction surface 32 of the brake lining 26 and the braking surface 18 on the drum 12. The pedal feel for a vehicle operator remains generally constant if this predetermined distance is maintained. The interior cavity 36 has a first sloped or tapered section 42 at one end and a second sloped or tapered section 44 at an opposite end. The tapered sections 42, 44 extend in opposite directions such that the cavity is widest at the ends and narrowest at the center.
The adjustment mechanism 38 includes a first adjuster member 46 having a first mating tapered surface 48 for engaging the first tapered section 42 of the lining interior cavity 36. A second adjuster member 50 has a second mating tapered surface 52 for engaging the second tapered section 44 of the lining interior cavity 36. The adjusters 46, 50 are preferably made from a hardened steel.
The first adjuster member 46 includes a circular base 54, which extends to a distal end 56 of smaller diameter via the first mating tapered surface 48. On one side of the base 54, a plurality of holes 58 are formed to receive connecting shafts or torque rods 60, which will be discussed in more detail below. Each of the holes 58 preferably include a bushing (not shown) to allow free linear movement relative to the first adjuster member 46. The first adjuster member 46 also includes a first threaded bore 62 that extends through the center of the first adjuster member 46 from the base 54 to the distal end 56.
The second adjuster member 50 includes a circular base 64, which extends to a distal end 66 of smaller diameter via the second mating tapered surface 52. Around the periphery of the base 64, a plurality gear teeth 68 are formed which mesh with an adjuster actuator 70, which will be discussed in more detail below. A plurality of holes 72 are formed within the second mating tapered surface 52 to receive the torque rods 60. The rods 60 are preferably threaded into the holes 72 of the second adjuster member 50. Slots 61 are formed within the brake lining 26 in each block segment to receive the torque rods 60.
The torque rods 60 allow adjuster synchronization to occur between the first 46 and second 50 adjuster members. The rods 60 connect the adjuster members 46, 50 together to allow for equal rotational adjustment for each adjuster member 46, 50. The second adjuster member 50 also includes a second threaded bore 74 that extends through the center of the second adjuster member 50 from the base 64 to the distal end 66.
The first 46 and second 50 adjuster members are supported on a common cylindrical shaft 76 that has a threaded outer surface 78 and an interior bore 80. One of the threaded bores 62, 74 of the adjuster members 46, 50 has a left hand thread while the other threaded bore 62, 74 has a right hand thread. The threaded outer surface 78 of the cylindrical shaft 76 similarly has a first portion that is a left hand thread and a second portion that has a right hand thread. The right hand adjuster, i.e. the second adjuster member 50, should be slightly longer than the left handed adjuster to accommodate the adjusting mechanism. The longer right handed adjuster member 50 incorporates cone worm gearing on the outer diameter of the base portion 64, to allow for brake adjustment and to restrict shoe rotation.
The adjuster actuator 70 controls the adjustment mechanism 38. An electric motor 82 drives a cone worm gear 84 that meshes the cone worm gearing 68 on the second adjuster member 50. The worm gear 84 rides on ball bearings and is preferably case hardened for extended wear and to resist stress fatigue. The worm gear 84 is caged in a forged housing to prevent rotation of the brake lining assembly 26 during actuation. Worm gear rotation is accomplished by the electric motor 82, which is controlled by a central processor unit or other similar controller 86 (see FIG. 3) known in the art.
A linear translation sensor 88 gauges lining wear by measuring linear displacement during actuation. After a predetermined linear displacement value is sensed, the processor unit 86 actuates the worm gear electric motor 82 for lining adjustment. As the second adjuster member 50 rotates, the two adjuster members 46, 50 are pulled towards each other using the opposing threads. This forces the brake linings 26 outwardly to maintain the predetermined distance 40 between the friction surface 32 and the braking surface 18.
The brake shoe assembly 22 and adjustment mechanism 38 are supported on a common shaft 24. This shaft 24 is received within the central bore 80 of the cylindrical shaft 76 that supports the adjuster members 46, 50. The center journal shaft 76 is supported with linear bearings 90 to prevent rotation and allow linear translation of the brake shoe 22 and adjustment mechanism 38 during actuation. The journal shaft 76 rides on a modified axle end that is to be used as an inner bearing race. A left and right hand thread will be incorporated on the journal sleeve to allow for adjuster cone 46, 50 adjustment. Also incorporated in the center of the journal is an alignment ring 92 to keep proper shoe geometry.
During a braking interval or brake actuation, the whole mechanism, the shoe assembly 22 and the adjustment mechanism 38 slide on the shaft 24 to engage the friction surface 32 against the braking surface 18 of the drum 22.
Various types of brake actuators can be used to actuate the brake assembly during a braking interval. One embodiment, shown in FIG. 3, utilizes a lever 94 that incorporates a fulcrum point 98 below the axle centerline 20. Two (2) wear pads 100 are formed on the lever 94 at the axle centerline 20 for brake actuation. The center of the lever end accommodates a shaft for actuation input force.
A second actuation method, shown schematically in FIG. 4, incorporates a screw threading engagement style actuator, shown generally at 102. This system requires that the drum 12 have two (2) degrees of freedom (rotational and linear translation) and the brake shoes 22 have one degree of freedom (linear translation). The system actuates the brake by pulling the drum 12 onto the shoes 22, as well as pushing the shoes 22 into the drum 12. With this type of actuator nearly 100 percent efficiency can be achieved.
A third method of actuation, shown in FIG. 5, can utilize the same principle as the second actuation method, except that an electromagnet 104 is used to engage the drum 12 and the brake shoe assembly 22 together.
This braking mechanism 10 is preferably used with on-highway heavy vehicles where air brakes are commonly utilized. This braking mechanism uses a conical design that enables more lining material to be packaged in the brake drum 12 than in conventional brakes, while reducing actuation energy requirements. The addition of extra lining material lengthens time between servicing intervals to reduce maintenance costs for fleets. The conical brake drum 12 and corresponding lining 26 allows for a possible 5:1 mechanical advantage, which equates to lower brake input actuation forces while still achieving the performance of a conventional S-cam brake. Brake actuation is carried out by linear translation of the brake shoe 22 and adjustment assembly 38 into the brake drum 12. Brake shoe assembly 22 movement is controlled with the use of linear bearings 90, which allow horizontal movement and restrict rotational movement of the shoe assembly 22 during braking.
The braking mechanism 10 operates in the following manner. The brake shoes assemblies 22 are comprised of four sections that can expand outward to compensate for lining wear and incorporate retaining springs 34 set in a circumferential groove 35 to keep the package together. Preferably, a single circumferential spring 34 is mounted within the groove 35 around the ends of the sections to retain the four sections together, however, other similar springs known in the art can also be used. The spring 34 is pinned to each section. Preferably, the groove 35 is Teflon.RTM.coated to form a slidable surface.
Lining adjustment is accomplished with the use of two conical adjusters 46, 50 that move inwards toward each other to expand the brake shoes 22. Adjuster movement is accomplished by rotation of a worm gear 84, which in turn rotates and adjusts the conical adjusters 46, 50 with the use of left and right hand threads on a common shaft 76. Adjuster synchronization is accomplished with the four (4) horizontal rods 60 connecting the adjusters 46, 50 together, which allows for equal rotational adjustment for each adjuster. The connecting shafts 60 are threaded into the primary adjuster and are allowed free linear movement in the secondary adjuster to allow for adjustment.
Brake actuation is accomplished with the use of a simple lever 94 that translates the lining assembly 26 into the drum 12 to provide a braking force. A center ring 92 on the journal shaft 76 is used to control shoe geometry linearly to prevent misalignment during actuation. The benefits of the new arrangement include the ability to increase lining material for extended brake life before servicing, as well as reducing brake actuation forces.
Although a preferred embodiment of this invention has been disclosed, it should be understood that a worker of ordinary skill in the art would recognize many modifications come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.
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